Background

I have long wanted to start doing moonbounce, known as Earth-Moon-Earth (EME), as I felt it represented one of the most challenging parts of the hobby. It's almost at the extreme sports end of it in fact, everything has to be bigger, better, and well engineered, compared to other parts of the hobby. Having worked DX on most bands from 10m up to 3cms in my time, I needed a new challenge.

I first operated on EME in 1992 on 2m from the shack of Dave G0LBK. It was done using CW, very narrow receive filters, very high powers and whopping great Yagis. I worked three stations, two being in the USA and one in Germany. Although very impressive, it was not the direction that I wanted to go. The advent of weak signal digital modes for EME in the early 2000s piqued my interest and made the barrier to entry into EME much lower than before. I contemplated a 23cms EME system using a few hundred Watts and a 3m dish. To this end I bought a suitable dish feed from OK1DFC but then real life got in the way, and the feed stayed in its box for the next twenty years!

The path length to the moon is approximately 250,000 kms each way, and the Moon is a rather poor reflector too. This means that the path loss, which is frequency dependent, is very high indeed and needs to be overcome to stand any chance of working people.

2024 Arrives

I bought at IC-905 towards the end of 2023 nominally for operation using microwaves on hill tops, it can operate anywhere from 2m to 3cms excluding 9cms. It has built-in GPS frequency stabilisation, and is a rather lovely piece of equipment, to be fair, for the price I would hope so. I would have used my IC-9700 with the Leo Bodnar GPS frequency stabilisation added, but I felt that the IC-905 offered more. They both provide 10 Watts on 23cms as standard. So the IC-905 was chosen as the prime mover for EME. From reading the EME FaceBook groups I found that a few others used that radio to good effect, particularly Dave KG0D.

I still needed more though. Including:

• Dish
• Dish feed
• Power amplifier
• Preamplifier
• Dish rotator
• Dish mount
• Sequencer
• Sundry bits and pieces

The Dish

Although you can buy suitable dishes new, notably from RF Ham Design, they are expensive. My friend Dave G0LBK (see above) put me in contact with a G8 selling a 2.4m dish made by RF Ham Design. The dish came with feeds for 23cms and 13cms and simple elevation control. This was ideal and with some work could be adapted for EME operation.

The Dish Feed

In the early 2000s, OK1DFC came out with the design of the Septum Feed for EME operation. This was notably simpler than previous designs and created the required circular polarisation for EME. The sense of the rotation being the opposite for transmit and receive. This is because for a typical EME path the wave is reflected three times, at my dish, at the moon, and at the far dish. With every reflection the sense of the circularity is reversed, so the received signal is always opposite from that transmitted.

The Septum Feed design did all this without the complexity of RF splitters and combiners as used by previous designs. Indeed the Septum Feed is almost completely ubiquitous on 23cms EME at this time.

Luckily I had one of these dish feeds already so I just needed to find it in my storage unit, which I managed to do.

The Power Amplifier

I wanted to have at least 200 Watts for EME, but with the use of digital modes where the transmission time can be up to two minutes, I really needed a much larger amplifier that I could underrun to ensure that it would survive the long overs of continuous carrier.

Roger G4BEL was a well known operator in the Cambridge area, unfortunately he became a silent key in 2024 and his equipment was disposed of. Amongst it was a 600 Watt DB6NT amplifier already built into a rack case with fans and all of the required DC switching. Just provide 28 Volts at lots of Amps and some RF and off you go. For full output about 18 Watts is required so my IC-905 at 10 Watts will never push it to full power. The amplifier was bought, along with some other bits and pieces.

The Preamplifier

I had hoped to buy a G4DDK preamplifier which are state of the art, but Sam has stopped making them. I therefore sourced a WD5AGO preamp from Texas which promised to have similar performance, typically a noise figure of between 0.2 and 0.3 dB and a nice high gain from a two stage design. I also bought an old DB6NT preamplifier from the G4BEL SK estate which has a noise figure of around 0.7 dB as a standby.